topic Re: #pragma pack(1) supported? in MQX Software Solutions

#pragma pack(1) supported?

MarkP_ — Wed, 09 Nov 2011 20:57:43 GMT

Hi,

How to tell CW compiler to pack structs?

#pragma pack(1) gives an "Illegal pragma" warning and does not pack variables.

The compiler generates dummy byte between variables:

typedef struct {
uint_8 channel;
uint_16 value;
}ADC_Value_t;

When communicating with other systems the struct need to be packed.

~Mark

Re: #pragma pack(1) supported?

BryGuyH — Thu, 10 Nov 2011 00:13:25 GMT

Its been a while but I thought CW used

#pragma options align=packed

#pragma options align=reset

pairs?

Re: #pragma pack(1) supported?

DavidS — Thu, 10 Nov 2011 05:05:24 GMT

Hi Mark,

I found out how to do two things: turn on checking for structures being padded and how to ensure the structure parameters are packed. I haven't found out how to globally set the packing option.

The below #if has comments to explain.

#if

1 //DES test for customer MarkP from forums

#pragma

warn_padding on //turns on warning but have to visually check if you get a warning...other settings [off | reset].

typedef

struct{

volatileuint_8channel__attribute__((aligned (1))); //DES changing 1 to a 4 and recompile to see warning

volatileuint_16value__attribute__((aligned (1))); //DES not really needed but if you were to add to struct handy to already have in code

}

ADC_Value_t;

#endif

Warning in console when aligned(4):

(C:\Freescale\FreescaleMQX3.7\mqx\examples\adc\adc_demo.c|158|1|11|6463|11)

=}ADC_Value_t;

>1 pad byte(s) inserted after data member 'value'

Alternatively you could turn on the Pad Bytes Added (full) option in the ARM compiler Warnings settings and you will see a number of struct warnings about bytes being padded.

Hope this helps.

Regards,

David

Re: #pragma pack(1) supported?

LuisCasado — Thu, 10 Nov 2011 05:57:01 GMT

Hello,

You can use the following approach to align the struct:

typedef struct
{
unsigned long ChunkID __attribute__((aligned (4)));//4 bytes = "RIFF" 0x52494646 big-endian form
unsigned long ChunkSize __attribute__((aligned (4)));//4 bytes
unsigned long Format __attribute__((aligned (4))); //4 bytes = "WAVE" 0x57415645 big-endian form
unsigned long Subchunk1ID __attribute__((aligned (4))); //4 bytes = "fmt" 0x666d7420 big-endian form
unsigned long Subchunk1Size __attribute__((aligned (4))); //4 bytes
unsigned short AudioFormat __attribute__((aligned (2)));//2 bytes: 0 =???; 1 = Linear quantization; Others = compression
unsigned short NumChannels __attribute__((aligned (2)));//2 bytes: Mono = 1; Stereo = 2; etc.
unsigned long SampleRate __attribute__((aligned (4)));//4 bytes: 8000, 44100, etc.
unsigned long ByteRate __attribute__((aligned (4)));//4 bytes: SampleRate * NumChannels * BitsPerSample/8
unsigned short BlockAlign __attribute__((aligned (2)));//2 bytes: NumChannels * BitsPerSample/8
unsigned short BitsPerSamples __attribute__((aligned (2)));//2 bytes: 8 = 8 bits; 16 = 16 bits; etc.
unsigned long Subchunk2ID __attribute__((aligned (4)));//4 bytes = "data" 0x64617461 big-endian form
unsigned long Subchunk2Size __attribute__((aligned (4)));//4 bytes: NumSamples * NumChannels * BitsPerSample/8
unsigned char x __attribute__((aligned (1)));
// unsigned long Data;//(ChunkSize) bytes
} WAVE_FILE;

Best Regards,

Luis

Re: #pragma pack(1) supported?

MarkP_ — Fri, 11 Nov 2011 00:43:12 GMT

Thank you for your answers.

There is also another potential problem, is the uint_16 variable big or little endian.

Is it compatible with another system?

Solved like this:

typedef struct {
uint_8 channel;
uint_8 valueHi;

uint_8 valueLo;
}ADC_Value_t;

~Mark

Re: #pragma pack(1) supported?

mpc8377e — Mon, 19 Mar 2012 19:55:51 GMT

Hi,

I have aligned structure members something like this:

struct USB_SysInfoResponse
{
   uint_16 version;// __attribute__((aligned (2)));
   uint_8 configuration __attribute__((aligned (1)));
};

After doing this i can still get the size of struct as 4bytes, the result should have been 3bytes.

To have effect fo __attribute what needs to added in the code?

Regards,

Raghu